Numerical control (NC) refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via hand wheels or levers, or mechanically automated via cams alone. The first NC machines were built in the 1940s and 50s, based on existing tools that were modified with motors that moved the controls to follow points fed into the system on paper tape. These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern computer numerical controlled (CNC) machine tools that have revolutionized the manufacturing process.
In modern CNC systems, end-to-end component design is highly automated using CAD/CAM programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different operations—drills, saws, routers, gluing, assembly, hardware insertion, end treating, etc.—modern machines often combine multiple operations into a single “cell”. In other cases, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case, the complex series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.
Double end machines, such as a double end tenoner, include a conveyor for moving components from work station to work station. As the components are moved past each work station, a different machining operation is performed on the end or ends of the component. In these double end machines, a transport mechanism conveys the component from work station to work station. The transport mechanism is positioned to hold the ends of the component during machining operations. One side of the double end machine has fixed position machine tools. The other side of the double end machine is adjusted for the length of the component or work piece. All stations on the adjustable side move together so that once adjusted, the machine tools associated with that side of the station are positioned to work on the same width work piece or component. These double end machines are good for manufacturing a multiplicity of work pieces or components of the same width. However, these machines are inefficient if small numbers of components of a set width or dimension are to be manufactured. When a substantially different width component needs to be manufactured, the entire machine must be cleared of any component of a different length than the next component to be manufactured. After clearing, the entire side including half the machine tools must be adjusted to the new width. In other words, once the machine is set up, components or work pieces of the same length are fed into the double ended machine as part of a production run. Changing the length or width of the component requires some down time to set up the machine again for a different length or different width component. The amount of downtime depends on how many stations are associated with the double end tenoner. When manufacturing one finished part at a time, the clearing time per part can become a higher than desired amount of time taken from production. In other words, if production runs are low in number, the downtime necessary to reset the machine makes manufacturing inefficient. In addition, production of the type where there are large production runs requires carrying large inventories of produced parts awaiting assembly into the final product. The current trend in manufacturing is just in time manufacturing where the part is made and then used or shipped. In this way, the cost of inventory goes way down since the inventory processed from raw materials into the final part is minimized.